Temporomandibular Joint

Learning Objectives

Describe the gross anatomy of the temporomandibular joint.
Explain the sensory innervation of the temporomandibular joint.
Describe the neuromuscular contributions of temporomandibular joint movement.
Given a clinical example, provide an appropriate anatomical explanation.

Overview of the Temporomandibular Joint

The temporomandibular joints (TMJs) and related structures play an essential role in mastication (chewing). The act of chewing is resultant from coordinated neuromuscular interaction between cranial nerves of the central nervous system, muscles of mastication, tongue, teeth, and the paired TMJs. The TMJ complex is also involved to some degree in speaking and swallowing.

Anatomy Overview

The TMJ is classified as a ginglymoarthrodial joint (displays both hinge and sliding capabilities).
- Movements at the joints are referred to as rotational (hingelike) and translational (sliding).
- Bony components of the TMJ (bilateral on the skull).
  - Superior: the concave mandibular fossa (also known as the glenoid fossa) and articular eminence of the temporal bone.
    - During mastication, joint contact/compression occurs along the slope of the articular eminence due to translational/sliding movement of the joint, not at the concave roof of the mandibular fossa (common misconception).
  - Inferior: the convex mandibular condyles.
    - The articular surfaces are covered with dense fibrous connective tissue in adults.
Dental (teeth) occlusion and TMJ positioning (location of the mandibular condyles) are interrelated ().
- Connective tissues:
  - A dense fibrous articular disk sits between the bony components of the TMJ. This oval disk is shaped to fit optimally between the mandibular condyle and the articular eminence of the temporal bone.
    - The disk is thicker anteriorly and posteriorly, which helps it maintain position over the mandibular condyle.
    - Only the disk periphery is innervated and vascularized ().
    - Circumferential disk attachment to the surrounding joint capsule creates superior and inferior joint cavities ().
      - Synovial cells line the inner layer of the TMJ capsule and produce fluid for each cavity.
      - Anterior/posterior translational or “sliding” joint movements occur in the superior cavity.
        
        Superior cavity is the space between the disk and the temporal bone articular eminence.
      - Rotational/hinge movement occurs in the inferior joint cavity.
        
        Inferior joint cavity is the space between the mandibular condyle and the disk.
    - A retrodiskal tissue (pad) is attached to the posterior aspect of the disk/capsule.
      - It has two layers, an elastic superior retrodiskal lamina (SRL) and nonelastic inferior retrodiskal lamina (IRL; see ).
    - Anteriorly, the capsule and disk fuse.
      - The superior portion of the lateral pterygoid muscle also has fibers inserting into this area.
    - Medial and lateral aspects of the joint capsule and disk are attached to their respective condyle poles via lateral collateral and medial collateral ligaments.
  - Two accessory TMJ ligaments (sphenomandibular and stylomandibular) help suspend the mandible from the skull. They are located medial to the joint and oriented in an anterior and inferior direction from the skull base ().
    - The sphenomandibular ligament may also help limit lateral mandibular movement.
    - The stylomandibular ligament may help limit end range mandibular protrusion.
    - Overall, accessory ligament contributions to typical masticatory function appear to be limited.
Vascular supply of the TMJ.
- Provided by branches of the external carotid artery found near the joint.
  - Most commonly cited vascular contributions to the TMJ include:
    - Superficial temporal.
    - Maxillary.
    - Anterior tympanic.
    - Deep auricular.
    - Additional potential contributions, less commonly noted:
    - Transverse facial.
    - Middle meningeal.
    - Ascending pharyngeal.
A key consideration for mandibular surgery and trauma management: the primary blood supply to the condylar heads of the mandible is the inferior alveolar artery on each side ().
- The inferior alveolar artery enters the bone at the mandibular foramen and supplies the bone marrow and the cortical bone of the entire mandible.

Fig. 23.1 Occlusion influences positioning of the mandibular condyle and disk. (Modified with permission from Gilroy AM, MacPherson BR. Atlas of Anatomy. Third Edition. © Thieme 2016. Illustrations by Markus Voll and Karl Wesker.)

Fig. 23.2 Anatomy of the temporomandibular joint (TMJ). The intra-articular disk creates a superior and inferior joint space.

Fig. 23.3 Posterior attachments of the temporomandibular joint (TMJ) disk.

Fig. 23.4 Ligamentous structures contributing to the temporomandibular joint (TMJ) stability. (Reproduced with permission from Gilroy AM, MacPherson BR. Atlas of Anatomy. Third Edition. © Thieme 2016. Illustrations by Markus Voll and Karl Wesker.)

Fig. 23.5 Arterial supply of the temporomandibular joint (TMJ).

TMJ Sensory (Afferent) Innervation

Hilton’s law is an excellent tool for understanding joint innervation. It states that a joint will receive sensory innervation from the nerves that supply the muscles that cross and act on the joint.

The primary source for sensory innervation of the TMJ capsule (see ) is branches of the mandibular division of the trigeminal nerve (V₃).
- Auriculotemporal nerve is the most commonly cited source of sensory innervation.
- Additional branches of V₃ that may also provide afferent TMJ innervation:
  - Masseteric nerve.
  - Deep posterior temporal nerves.
  - Great auricular nerve from the cervical plexus (C2–C3):
    - May also innervate part of the TMJ and surrounding anatomy due to proximity of the dermatome and potential for sensory overlap between this nerve and V₃.
- Sensory receptors/nerve endings in the TMJ:
  - Primarily free nerve endings.
  - •Some Ruffini’s nerve endings, Golgi–Mazzoni corpuscles, and Pacinian corpuscles are also present ().